In traditional radio networks for wireless communication, such as GSM networks, a single narrowband frequency carrier is typically used for transferring data and messages in radio signals between the network and a user node connected to a radio access node of the network, usually called network node or base station, either for transmitting signals from the network node on a downlink connection to the user node or for transmitting signals from the user node on an uplink connection to the network node. Recently, increasingly advanced user terminals and devices have emerged on the market, e.g. smartphones, tablets and wireless laptops, which are suitable for services such as internet browsing, streaming of media and any other communication of large amounts of data. The demands for high data throughput has therefore increased.
In this description, the term “user node” is used to represent any communication equipment capable of transmitting radio signals to a radio access node of a radio network, such as a base station. The user node in this context could also be referred to as a mobile terminal, mobile station, User Equipment (UE), wireless device, etc., depending on the terminology used. Further, the term “network node” will be used to represent a node of a radio network, that is configured to signal information to a user node.
To meet the greater demands for data throughput, the possibility of using two or more carriers in parallel in a user node has been introduced such that the amount of data that can be communicated per time unit, also referred to as data throughput, is basically multiplied by the number of carriers used. This feature thus introduces multiple parallel carriers transmitted on separate frequencies to or from the same user node, provided that the user node is capable of using multi-carriers. The user node may also employ multiple antennas for transmitting on multiple carriers. Further, the user node may need to switch between two different operating modes such as transmitting on a single carrier or on two or more carriers, basically depending on availability of radio resources and/or the need for data throughput.
Uplink transmissions from a first user node which occur within a first system band may cause interference to one or more other nodes receiving radio signals within a neighboring second system band since the first user node's transmission also causes unwanted emissions outside its own nominal transmission band, also referred to as “out-of-band” or “spurious” emissions. For example, the first and second system bands may be used by different network operators having adjacent licensed frequency bands, or by different cells of a radio network. An example situation is illustrated in FIG. 1 where a first network system 1 is configured to use a system band for uplink transmissions and a second network system 2 is configured to use a neighboring system band for either downlink or uplink transmissions or both.
Even though the uplink band of system 1 and the band used by system 2 are separated by a certain guard band in the example shown in the figure, transmission from the first user node in the uplink band of system 1, denoted “aggressor”, may still cause interference to a second node receiving in the neighboring band 104 of system 2, denoted “victim band”. The unwanted emissions on both sides of the nominal uplink band 100 are schematically indicated by dotted curves outside the band 100, and a part 102 of the nominal victim band 104 of system 2 coincides with the emissions from the first user node, thus resulting in interference at the second node, particularly if the first and second nodes happen to be located relatively close to one another.
For example, the victim band 104 may be used for downlink transmissions and the second node may therefore be a user node. A similar interference from uplink emissions may also occur when the victim band is also used for uplink transmissions where the second node is a network node. Another example is when the victim band 104 is used for Time Division Duplex, TDD, transmissions alternately switching between downlink and uplink timeslots according to a TDD scheme. Further examples include when the victim band 104 is used for other wireless services such as public safety, military communication, radar, and so forth.
It is thus a problem that uplink transmissions in a nominal band may cause interference in another adjacent victim band due to unwanted out-of-band emissions that partly coincide with the adjacent victim band. A conventional solution to avoid or at least reduce the above interference is to employ power regulation such that the transmitting user node is instructed by its serving network node to reduce its transmission power. This may be implemented by sending or otherwise providing a maximum allowed transmit power to the user node, thereby instruction the user node to use a transmit power not exceeding the maximum allowed transmit power. This maximum allowed transmit power may also be preconfigured, e.g., in a standard specification or the like. However, if the user node frequently switches between different operating modes, the network node may need to send a new power regulation order each time the user node has switched its operating mode.
It is thus another problem that if a user node switches between different operating modes, the serving network node may need to send frequent power regulation orders to the user node which occupy precious radio resources, and it also takes some time before the user node has received an order and adjusted its transmit power accordingly. Therefore, the user node may still generate the above-described unwanted emissions that may cause interference in an adjacent band, at least for a limited time period before adopting to the power regulation order, each time it has changed its operating mode which may be done repeatedly and very rapidly, e.g. depending on the current need for data throughput and available radio resources.